Within every digital integrated circuit there will always be one data path between two circuit blocks that requires the longest time to generate the proper output data before the data may be sampled. This occurs due to propagation delays caused by the complex logic circuits between flip-flops. The data path that requires the longest time for the data signal to be generated before it may be sampled is known as the critical "speed path" of the integrated circuit.
The maximum speed that the digital integrated circuit may operate at is limited by the speed path in the digital integrated circuit. The reason for this is that the speed path presents the longest delay path thus the clock rate can not be increased beyond the point where the clock cycle time is equal to the propagation delay of the speed path.
Since the maximum speed of an integrated circuit is limited by the speed path of the integrated circuit, it is very desirable to be able to easily locate the speed path within an integrated circuit. However, in complex modern integrated circuits such as microprocessors there are millions of possible paths that may be the speed path. To locate the speed path among the millions of data paths in the integrated circuit requires sophisticated design and testing tools